1. Field of the Invention
This invention generally relates to a fuse structure for a semiconductor device, and more particularly to a fuse structure having multi-blocks for a semiconductor device.
2. Description of Related Art
As the size of a semiconductor device becomes smaller, the semiconductor device is more seriously affected due to impurity or defects in itself. A defect of a single diode or transistor may cause the whole chip to fail. To solve this problem, some redundant circuits connected to fuses generally will be added into the circuit. When a defect is found in a circuit, the fuses can be used to disable the defected circuit and enable the redundant circuit. For memory devices, the defected cell can be replaced by a non-defected cell to its address. Another reason to use fuses in the integrated circuits is to permanently write the controlling bytes such as ID codes into the chip.
Generally, the fuses are made of polysilicon or metal materials. Laser fuses and electronic fuses are two major types of fuses based on how the fuses are blown. The laser fuses will be blown by the laser beam; and the electronic fuses will be blown by currents. The electronic fuses are generally applied to EEPROM devices, while the laser fuses are generally applied to DRAM devices.
Generally, an integrated circuit has a passivation layer including silicon nitride, silicon oxide or both at the top thereof. To prevent the passivation layer from damage, an opening at the top layer is required and the laser beam has to focus precisely on the fuse in order not to damage the adjacent devices. However, it is common that the passivation layers neighboring to the fuses are damaged due to the strong power of the laser beam.
For the electronic polysilicon fuse application, it requires a high voltage to generate a current that is adequate to heat and rupture the fuse. When the size is getting smaller, the voltage required for blowing the fuse can be correspondingly decreased. Hence, a silicide layer is arranged on the polysilicon fuse so that an appropriate voltage can blow the fuse. Since the heat generated by the current can enhance the electron migration, the silicide layer and the polysilicon fuse will agglomerate together to make the silicide layer rupture and the grains of the polysilicon re-grow.
For the fuse to be open, either the fuse must be ruptured, or the silicide layer on the polysilicon fuse fused, or the post-burn resistance of the polysilicon fuse must be so high that the fuse may be deemed open.
As the conditions of the manufacturing process and the applied voltage frequently change, even after applying the voltage to blow the fuse, the remaining fuse may be found or the post-burn resistance is not stable, which affects the reliability and the performance of the devices. Further, the heat generated by the current my also deteriorate the adjacent devices and affects their reliability.